Sepsis is a serious medical condition caused by an overwhelming response of the host immune system to infection. It can trigger widespread inflammation, which can give rise to impaired blood flow. As sepsis progresses, the body's organs can be starved for oxygen and nutrients, causing permanent damage and eventual failure. Left improperly diagnosed or otherwise untreated, the heart may weaken and septic shock can occur, leading to multiple organ failure and death. Blood cultures are required to detect the presence of bacteria or yeast in the blood of sepsis patients, to identify the microorganism(s) present, identify antibiotic susceptibilities, and guide treatment. Positive blood cultures (“PBC”) are used to identify the microorganism(s) and perform antimicrobial susceptibility testing (“AST”). In order to identify the microorganism(s) and perform susceptibility testing, intact, viable microorganism(s) need(s) to be isolated from the blood cells and other debris in the collected sample.
Current techniques for isolating viable microorganism(s) from a PBC sample often utilize liquid separation methods containing lysis buffers with detergents that lyse the blood cells in the PBC sample. After lysis, the lysed blood cells can be removed while the viable microorganism(s) is/are retained. However, the use of these lysis buffers often result in non-viable microorganism(s) which is/are insufficient for performing certain biochemical testing such as AST testing. This is particularly true for Streptococcus pneumoniae (S. pneumoniae), which is often difficult to isolate and identify. Ultimately, time consuming methods, such as sub-culturing of the microorganism(s), are required in order to obtain a plated pure culture of viable microorganism(s). Preparation of a plated pure culture can take up to 48 hours which may result in many of the septicemia patients being initially treated with inappropriate antibiotics.
Accordingly, it is desirable to develop methods that rapidly separate microorganism(s) from a PBC sample while maintaining the viability of the microorganism(s), so that analytical methods that require cell viability, such as AST testing, can be performed. Additionally, it is desirable that these methods do not contain any substances which would interfere with methods of identifying the microorganism(s), for example mass spectrometry. Ideally, the desired methods would allow for the rapid isolation of viable microorganism(s) from a single PBC sample that can be used for multiple down-stream analysis, such as, both identification by mass spectrometry and AST testing. In addition, the methods should be able to identify a wide panel of microorganisms, including the most difficult of organisms to identify, for example S. pneumoniae. 